We need more than just extra water to save the Murray-Darling Basin

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The Murray-Darling Basin is an incredibly complex ecological system.
Mike Russell/Flickr, CC BY-SA

Max Finlayson, Charles Sturt University; Lee Baumgartner, Charles Sturt University, and Peter Gell, Federation University Australia

After a long and contentious public debate, in 2012 Australia embarked on a significant and expensive water recovery program to restore the Murray-Darling Basin’s ecosystems.

Despite general agreement that a certain amount of water should be reserved to restore the flagging river system, the argument continues as to whether this should be 2,750 or 3,200 gigalitres (GL) a year, and how these savings can be achieved.

A recent report by the Wentworth Group of Concerned Scientists argues that there is no conclusive evidence, after five years, that the plan is effective. The report’s authors believe that an extra 450GL of water a year needs to be recovered to save the basin.

There is no doubt in our minds that the Murray-Darling river system is in crisis, and the Basin Plan was vitally needed. But while we broadly agree with the Wentworth Group’s report, it’s a mistake to focus on water volume alone.

Without giving equal attention to improving water quality and building critical ecological infrastructure, it’s possible that increasing river flows could actually harm the Basin.

What are we trying to recover?

We don’t really have much information on the state of the basin before industrial development. Most knowledge is more recent, but we do know that from about the 1920s onwards, considerable volumes of water have been removed. Few comprehensive historic records of flora and fauna, let alone water quality, are available.

While knowledge of the state and significance of the ecology of the river systems is scant, there is ample evidence that increased levels of nutrients, salts and, in particular, sediments have adversely affected the wetlands, main channels and associated floodplains.

The records of fish that historically lived in the rivers, billabongs and wetlands also tell a cautionary tale. These wetlands and rivers once teemed with native fish. In 1915, a single scoop of a 10 m seine net would yield more than 100,000 native fish in a single wetland.

There were dozens of species at each site, supporting a burgeoning fishery that was considered inexhaustible.

An example of extreme overfishing of Murray cod in the late 1800s, which caused the first strong declines in the species. Such catches were typical for the period.

Since that time the basin has been extensively developed. The fishing industry expanded, forests were cleared, dams were built, floodplains were blocked by levies, water began to be diverted for irrigation, the demand for drinking water increased and invasive species were introduced. But somewhere over the past 100 years we crossed a threshold where the system stopped being able to support native fish.

Nowadays, visiting the wetlands that were historically packed with native fish (all of which had huge cultural importance to traditional owners), we find mostly invasive species such as carp, goldfish and weatherloach.

In some places, native species that were once abundant have not been seen in 40 years. The formerly productive commercial fisheries, and the livelihoods they supported, have been shut down.

Our native fish are in trouble, and unless urgent action is taken, many face extinction within decades.

Rebuilding a complex system

The Basin Plan is underpinned by a focus on river volume as the cause of system degradation and subsequent recovery. But the system is much more complex than that. Fluctuating levels of sediments, salts and nutrients drive significant changes, and so regulating river flows – which carry these components from place to place – fundamentally alters the dynamics of main channels and floodplain wetlands.

Over the last century, erosion has filled the rivers in the Murray system with mud. When this water flows into the wetlands, this sediment builds and blocks the light, killing the aquatic plants that support native fish.

Simply increasing the water flow without addressing water quality runs the risk of exacerbating this problem. We therefore argue the first step in river recovery is attending to water quality.

The Murray-Darling Basin Plan has focused very heavily on the amount of water in the system; partly because speaking in terms of volume is easiest to demonstrate and understand. But the paleoecological record reveals that water quality, at least in wetlands, declined well before human use of water changed the river flows.

So if recovering water volume is a critical target, it is equally important that this water is of good quality. Recent experience with blackwater events, in which oxygen levels drop so low that fish suffocate, highlights this need. Even water of the wrong temperature, known as “thermal pollution”, can cause real harm. Winter-temperature water, for example, can prevent fish from breeding if it occurs in summer. Bad water quality will simply not provide good ecological outcomes.

A century of engineering development has fundamentally changed the basins rivers in a way that does not support native fish or the original ecology in general. Even if the recovered water is of high quality, we will need to take other steps to achieve tangible outcomes. Thus we need “complementary measures”, which augment the benefits of increasing river volumes. These include:

  • Mitigating thermal and other pollution to ensure the water temperature and overall quality is adequate,
  • Building fishways so that fish can navigate dams and weirs,
  • Restocking threatened fish species into areas they are no longer found,
  • Controlling carp and other non-native species that now dominate our waterways;
  • Building fish-friendly irrigation infrastructure such as screens on irrigation pumps or overshot weirs; and
  • Improving habitat through resnagging or controlling harmful practices on flood plains.

Another measure to improve the basin’s waterways, the proposal to release a virulent strain of carp herpes, has raised debate over whether it will neatly solve a major environmental and economic problem or create further issues.

If implemented correctly, these complementary measures are just as important as water recovery and improving water quality for meeting the basin plan’s ecological targets.

The ConversationRepairing a river system such as the Murray-Darling is incredibly complex, and we must broaden our view beyond simply thinking about water volumes. Some of these extra steps can also provide benefits with less cost to the people who live and work with the water. To achieve this we suggest a staged program of recovery that allows the communities who live in the basin more time to adapt to the plan.

Max Finlayson, Director, Institute for Land, Water and Society, Charles Sturt University; Lee Baumgartner, Associate Research Professor (Fisheries and River Management), Institute for Land, Water, and Society, Charles Sturt University, and Peter Gell, Professor of Environmental Management, Federation University Australia

This article was originally published on The Conversation. Read the original article.

The winners and losers of Antarctica’s great thaw

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Adélie penguin at the Mt Siple breeding colony, West Antarctica.
Jasmine Lee, Author provided

Jasmine Lee, The University of Queensland; Justine Shaw, The University of Queensland, and Richard Fuller, The University of Queensland

When you think of Antarctica, you probably picture vast, continuous ice sheets and glaciers, with maybe a penguin or two thrown in. Yet most Antarctic plants and animals live in the permanently ice-free areas that cover about 1% of the continent. Our new research predicts that these areas could grow by a quarter during this century, with mixed prospects for the species that currently live there.

Besides everyone’s favourite Emperor and Adélie penguins, terrestrial Antarctic species also include beautiful mosses, lichens, two types of flowering plants, and a suite of hardy invertebrates such as nematodes, springtails, rotifers and tardigrades, many of which are found nowhere else on Earth. Tardigrades – tiny creatures sometimes nicknamed “waterbears” – are so tough they can survive in space.

Antarctica’s ice-free areas are currently limited to a scattering of rocky outcrops along the coastline, or cliff faces, or the tops of mountain ranges. They form small patches of suitable habitat in a huge sea of ice, much like islands.

As a result, the plants and animals that live there are often isolated from each other. But as Antarctica’s climate warms, we expect ice-free areas to get bigger and eventually start joining up. This would create more habitat for native species, but also new opportunities for non-native species to spread.

Our study, published today in Nature, forecasts that climate change will expand Antarctica’s ice-free areas over the course of this century. Under the most severe scenario that we modelled (which is also the one on which the globe is currently tracking), more than 17,000 square km of new ice-free area could emerge across the continent by 2100.

This would increase the current total ice-free area by nearly a quarter. The majority of this new ice-free land will be on the Antarctic Peninsula, which could have three times as much ice-free area as it does today.

Projected Antarctic ice melt this century.
Lee et al. (2017) Nature

Brave new world

As the ice-free areas expand, the distances between them will decrease, giving plants and animals more opportunity to spread through the landscape. On the Antarctic Peninsula, which has already warmed more than anywhere else in Antarctica, many of the ice-free patches will expand so much that they will start joining together.

Will this increase in habitat availability benefit the plants and animals that live there? It will definitely provide new opportunities for some native plants and animals to expand their range and colonise new areas. The warming climate may also give a boost to species that are currently hampered by the lack of warmth, nutrients and water. Some Antarctic mosses, for example, are expected to grow faster as temperatures rise, and Antarctica’s two flowering plant species are already expanding southward.

However, the potential benefits seem likely to be outweighed by the negatives. The joining-up of habitat patches could allow species that have been isolated for much of their evolutionary past to meet suddenly. If the newcomers to a particular area outcompete the native species, then it may lead to localised extinctions. Over the coming centuries this could lead to the loss of many plants and animals, and the homogenisation of Antarctica’s ecosystems.

Antarctic aliens

An even bigger concern is that Antarctica’s great thaw could provide new opportunities for species to invade. Antarctica’s best bulwark against non-native species is its harsh climate and extreme weather, to which native Antarctic species have spent many thousands of years adapting.

A native Frisea springtail.
Melissa Houghton

We already know that many plants and invertebrates are reaching Antarctica, most often in food or cargo shipments. As the climate warms, some of these non-native species may be able to establish themselves on the Antarctic Peninsula, and the increasing connectivity will allow them to easily move through the landscape. Many of these animals and plants may become invasive, competing with the native species for space and resources.

We don’t know how Antarctica’s species will cope with the increasing competition. But if the sub-Antarctic islands provide any indication, the outlook is depressing. Australia’s World Heritage-listed Macquarie Island, for example, was severely impacted by invasive cats, rats, rabbits and mice (although it has since been declared free of these pests after an intensive eradication effort).

Several non-native species have already come to Antarctica, including the invasive annual meadowgrass Poa annua (a common weed around the world), which has colonised newly ice-free areas left behind by retreating glaciers. It is thought to outcompete Antarctica’s native plants, although we don’t yet know what the impact will be on animals.

Invasive meadowgrass on Macquarie Island.
Laura Williams

Humans – both scientists and tourists – are key transporters of non-native species to the continent, and tourist numbers continue to grow (almost 37,000 visited in the 2016-17 summer).

Biosecurity is paramount for the ongoing protection of Antarctica. If bags, shoes, clothes and field equipment are not properly cleaned and inspected before arriving on the continent, then non-native seeds, microbes and insects could be transported to Antarctica and begin to spread.

The ConversationWe call for protection of ice-free areas that will remain intact in a changing climate, and for the Antarctic scientific and tourism communities to pinpoint key areas where greater biosecurity and monitoring for invasive species may be needed.

Jasmine Lee, PhD candidate, biodiversity conservation and climate change, The University of Queensland; Justine Shaw, Conservation Biologist, The University of Queensland, and Richard Fuller, Associate Professor in Biodiversity and Conservation, The University of Queensland

This article was originally published on The Conversation. Read the original article.